1. Technical Field of the Invention
The present invention relates to a board for an electronic device, an electronic device, a ferroelectric memory, an electronic apparatus, an ink-jet recording head, and an ink-jet printer.
2. Description of the Related Art
As well known to those skilled in the art, an electronic device, such as a piezoelectric element used in an ink-jet recording head, a capacitor used in a ferroelectric memory, etc., generally comprises a pair of electrodes (an upper electrode and a lower electrode) and a ferroelectric layer made of a ferroelectric material disposed between the electrodes.
As the ferroelectric material, a metal oxide having a perovskite structure, which is represented by the composition formula ABO3, is used. In particular, lead zirconate titanate (PZT) having lead (Pb) as A, and a mixture of zirconium (Zr) and Titanium (Ti) as B, is widely used.
In the conventional electronic device, Pt has been used as the material for the lower electrode. Pt has strong self-orientation since it has a face centered cubic lattice (FCC) structure, which is a closest packing structure. Consequently, Pt still has strong orientation to (111) even when it is formed in the shape of a thin film on a layer made of an amorphous substance (hereinafter referred to as amorphous layer), such as SiO2, with the result that the orientation of the ferroelectric layer formed thereon becomes better.
Since Pt has extremely strong orientation, however, its crystal grain has a columnar structure, and its grain boundary is arranged vertically. As a result, Pb in the ferroelectric layer is apt to diffuse to a bottom part (for example, a lower electrode) along the grain boundary. Furthermore, adhesive property between the lower electrode and the amorphous layer is very poor.
An intermediate layer made of Ti may be disposed between the lower electrode and the amorphous layer (for example, SiO2 layer) to improve the adhesive property between the lower electrode and the amorphous layer, and a barrier layer made of TiN may be disposed between the lower electrode and the amorphous layer to prevent diffusion of Pb.
In the aforesaid cases, however, the electrode structure becomes complicated. Furthermore, Ti may be oxidized and Ti may be diffused to the lower electrode, with the result that the crystallinity of the ferroelectric material is lowered.
In case that the electronic device constructed as described above is applied to a piezoelectric element, an electrostriction characteristic is deteriorated. In case that the electronic device constructed as described above is applied to a capacitor, a hysteresis characteristic of polarized electric field (P-E), a leak current characteristic, a fatigue characteristic, etc. are deteriorated.
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a board for an electronic device, by which the electronic device with various excellent characteristics can be realized in the most suitable structure, an electronic device having such a board for the electronic device, a ferroelectric memory comprising such an electronic device, an electronic apparatus comprising the electronic device, an ink-jet recording head comprising the electronic device, and an ink-jet printer comprising the electronic device.